Yeah, my friend, you may a fuddy-duddy. "Guys" in the USA is a person and affectionate term. I guess it's understandable if you dislike the informality of the term, however, that irrational irritation identifies you as either a bit uptight or a fuddy-duddy.

I just consider "you guys" to be the second person subject pronoun, the plural of "you". It is simply a pronoun and nothing more, the "guys" portion by itself being stripped of all its original meaning. When people say "you guys", they never think, even for a moment, about the noun "guys" and its meaning. It has just become a new pronoun that has filled a very empty niche, if you consider that basically every other European language has a special word for the second-person plural (vosotros, vous, vosaltres, Sie...)

A similar process has taken place in Brazilian Portuguese with "a gente"... As any Romance language speaker can tell, this means "the people," but in Brazilian Portuguese it just means "we", the first-person plural pronoun. Nobody thinks of "the people" as they say it, it is simply like a new pronoun. The only difference is that this new pronoun didn't fill an empty niche, since "nós" still exists in Portuguese, so I'm not sure what the process was behind its use.

I remember that back in the 80s you had Canadians (which is where I'm from) using "gal" as the feminine of "guy". But "gal" isn't used in our dialect otherwise, so it seems to have been replaced by "girl".

The gender-neutral "you guys" seems to be filling in the same gap as "y'all": the need for a distinct second-person plural. And not just as a vocative either, because sentences like "No, really, I'd love to hang out with you guys this weekend but I've got family obligations" sound perfectly natural to my (northeastern US) ear. In direct address it can be shortened to "guys," but I think it's a completely separate usage from "the guys"/"that guy": as a noun it's an informal way to refer to a man, as a pronoun or plural marker for a pronoun it's gender-neutral and carries almost no meaning.

Interesting tidbit: while the word may have originated in the 19th century, its meaning was quite different, or at least varied widely between the US and the UK. And so when Gilbert & Sullivan poke fun at "the lady from the provinces who dresses like a guy" (and who "doesn't think she dances but would rather like to try"), they alas are not exposing an epidemic of cross-dressing in rural Victorian England, but referring to women festooned in ill-fitting finery until they resembled a Guy Fawkes effigy.

In her 60's, my mother, born in 1919, would say "This afternoon I am playing bridge with the girls". But she would have been offended if someone called her a girl. Today I think women in their 60's use this less often.

Referring to women as guys is done by younger women and many older women find this offensive.

Interestingly, a "girl" these days is less prone to calling a young man she's gushing over a "guy." They're now saying "boy." As in, "I met a boy" or "Who's the new boy?" And it's increasingly common to refer to one's boyfriend as "the boy." As in, "Just hanging on the couch with the boy" or "Got home and the boy had made me dinner!" It's particularly grating when women in their 40s refer to their husband as "the boy," but it happens.

It's getting complicated when girls are called "Guys" and a (recently disbanded) band from San Francisco, consisting of two guys, is called "Girls".
I notice myself starting more and more emails with "Hi folks", exactly to avoid this kind gender confusion.

I would trace the use in the UK of guys to refer to groups of females as well as males to the arrival of US TV programmes such as Friends.

After first being used by young people, ie the kind who watch Friends and the like, it is now pretty universal and has spread to young children (like by 5-year old son) and older, previously more conservative groups such as grandparents, primary school teachers and church ministers. I winced when the young, enthusiastic church minister called his congregation ¨you guys¨ for the first time.

Indeed, parents who address groups of young children as ¨kids,¨ ¨children¨ or ¨boys and girls¨ can now seem very old fashioned and rather formal.

It was common a few years ago in Yorkshire to refer to girls as 'tarts', though you would not have called them that to their face or there would have been serious bitching. The same was true (and may still be) in northern dialects of German: a Hamburger would call girls Deerns, the equivalent of standard German Dirnen, whores. Neither term was pejorative, though it was certainly carelessly sexist.

It is a bit like latin-based European languages that use the masculine third person plural to refer to groups of men (e.g. "Ils") or mixed groups and a different feminine third person plural to refer to groups of women ("Elles").

Or not, I don't know. My contemporaries would normally use 'gals' (rather than guys) to refer to a group of girls - and 'guys' to refer to a mixed group - but that may be a local thing.

I think that our UK family has used 'guys' for the whole group (5 siblings plus partners) since we were in our teens some half a century ago!

This is simply because there is no obvious alternative in many situations. Suppose you wish to say 'Hey guys shall we ..[do something interesting]'. 'Hey you' sounds too aggressive by far. Of course you might say 'Hey guys & dolls' but be prepared to duck!

Yet another word for "guy"-
In most anglophone places "geezer" is a synonym for "guy", "fellow", "bloke", etc. I would have no more hesitation in referring to a young male as "that geezer" than I would "that guy".
However, I recently discovered (well, it was new to me) that in the USA it has the additional implication of "old". To call someone a "geezer" is to call him "old".
The OED - "a man: he strikes me as a decent geezer
North American informal, derogatory an old man."
This is certainly not true elsewhere. People often refer to an "old geezer" but simply a geezer, unmodified, can be of any age.
In any case, I'd rather be called a geezer than a dude, which I find, for some reason, a really ugly word. As I find "bro". And "guy" when applied to a woman or girl.

Since the early 80s, I and others i know have used 'guy' for inanimate objects as well. As an electronics technisian, we might say; "try changing this guy out" or "this guy seems to be too hot", etc.
Also, on occasion, I have used 'folks' instead of 'y'all or guys.
Also, I believe I have read that the term 'guy' comes from references to effigies of Guy Fawkes being used by 'street urchins' to solicit pennies from passers-by. With cries of "a penny for the Guy" - so, it's origin is an object with male connotation.

To call a woman a "gal" is, whatever else, an indication that the speaker's youth is long past - 1950s at the latest.
It's like "chick", "filly" or "broad", the sort of word one could imagine Sinatra and the "Rat Pack" members' using.
Today, to call a woman a "gal" is to demontrate, unequivocally, that one is not a hepcat.
"Gal" or "gel" was also a late eighteenth or nineteenth century pronunciation of "girl" amongst the "fashionable classes". I think Flashman and his contemporaries may use it. But I don't think that's what you were asking about.

It may depend - I live in Scotland and frequently hear the Americanism "gals" as a quite common as a variant of "guys" - but for young female groups (i.e. in the same context as 'guys' - but when the group is entirely female).

I think the use of "gal" described above by Varq (perhaps "gels" when seen in literature) is more common within a particular strata of English society? (Sounds like the horsey set to me).

I and my mixed peer group (late 20's and early 30's) use "chick" all the time, more or less equivalent to "dude" in the sense of "I saw this chick with crazy pink hair" or "she's a pretty cool chick". Very informal and not pejorative. Also has all but lost its connection with "baby bird", and therefore is not patronizing the way I imagine it was when the Rat Pack used it.

Varq,
Thanks. I hadn't even known about "filly" before. "Chick" and "broad" I knew. "Gel" I am learning the very first time. Also your comment on "geezer" is interesting. I sort of intuit it probably meant someone old, but never bothered to double-check in a dictionary. "Dude" is an ugly word, I agree. The first time I heard it, I thought it was an obscene word like the other 4-letter words. Took me a long time to ascertain it wasn't. But still will never use it. For some reason, it just "sound" awful.

Speaking of gendered words in English, have 'car' and 'ship' lost their feminine gender. Remember when guys (male) would refer to their cars and ships as 'she'? Am I overgeneralizing to think that English is becoming sexless? lol

The anthropomorphizing of machines to which you refer has always been ridiculous and if your impression that it is dying out is correct - I haven't noticed it - then it can only be a good thing, indicating a small amount of "growing up".
I like and work with machines. I'm a mechanical engineer. But I've never thought of them as people or animals. Only man-made things.

Women often refer to groups of themselves and their friends as "girls," especially when being less serious, perhaps grabbing a bit of the freedom of youth. As in: "girls' night out", which is an event involving women of any age. (Guys do the same thing: "boys' night out" happens even with us Baby Boomer men in packs.)
And I have often incurred gentle wrath from a group of women whom I called "guys" without thinking. "Gals" and "ladies" receive no opprobrium, in my experience.